In the field of wireless communication, to enhance the performance of communication system and satisfy increasing requirements of data service by user, it introduces Orthogonal Frequency Division Multiplexing (OFDM) and Multiple-Input Multiple-Output (MIMO).
In the process of transmission, in order to further improve the transmission quality, firstly data flow and pilot frequency after MIMO coding can be pre-coded, and then can be mapped on different antennas to perform transmission. As such, dedicated pilot frequency occurs. In the MIMO system which adopts dedicated pilot frequency mode, an equivalent channel, which is after performing pre-coding, is obtained by utilizing channel estimation; for the system which needs to feedback the situation of a real channel, the equivalent channel needs to be transform into the real channel; however, the procedure of transforming the equivalent channel to the real channel is complicated, even it is unable to achieve. Moreover, for the terminal which has not any data transmission for a period of time, the situation of the real channel of that terminal cannot be obtained periodically. Therefore, it needs to measure the current situation of the real channel to satisfy the requirement of system feedback.
Measurement pilot frequency (also called MIMO midamble) refers to transmitting a specific pilot frequency sequence on a certain symbol of one frame, so as to perform the channel measurement at the receiving terminal. The channels at all carrier positions on the entire symbol can be estimated by using the MIMO midamble, so that it can be easy for the transmitting terminal to adopt a highly effective transmission policy reasonably according to the current situation of channels. In the wireless communication system, the situation of the real channel can be measured by utilizing MIMO midamble reasonably, such as feeding back Preferred Matrix Indication (PMI), Rank Indication (RI) of the channel when it is a Close Loop MIMO, feeding back Channel Quality Indication (CQI), Rank Indication (RI) of the channel and so on when it is an Open Loop MIMO, thus it is very important for improving the transmission efficiency of system.
In the advanced system based on OFDM technology, that is, the wireless resource structure of Advanced Air Interface (AAI), as shown in FIG. 13, wireless resource consists of superframe structure (20 ms) as a unit on the time, each superframe consists of 4 frames (5 ms), and each frame consists of subframes. The subframe can be divided into 4 types according to OFDMA symbol numbers included in the subframe, FIGS. 14, 15 and 16 represent the subframe structure of Type1, Type2 and Type3, respectively, which include 6, 7 and 5 OFDMA symbols, respectively.
For a Time Division Duplex (TDD) system, part of or all the subframes of each frame composes a downlink frame, and each subframe included in the downlink frame is called a downlink subframe; and for a Frequency Division Duplex (FDD) system, all the subframes of each frame composes a downlink frame and an uplink frame, in which each subframe included in the downlink frame is called a downlink subframe.
For the frame structure which only includes the advanced system, different frame structures can be conFIG.d by different bandwidths, different length of Cyclic Prefixes (CPs), different duplex manners and different ratios of the uplink subframe and the downlink subframe, such as some configurations as shown in FIG. 17-FIG. 20. FIG. 19 is the frame structure in which the advanced system and Wireless Metropolitan Area Networks (WirelessMAN) Orthogonal Frequency Division Multiple Access (OFDMA) system coexist, and at the time, uplink frames of the advanced system and uplink frames of the WirelessMAN OFDMA system are multiplexed in the form of TDM. FIG. 20 is the frame structure in which the advanced system and the WirelessMAN OFDMA system coexist, and at the time, uplink frames of the advanced system and uplink frames of the WirelessMAN OFDMA system are multiplexed in the form of FDM. In the drawings, DL/UL SFi (j) represents the (i+1)th subframe of downlink or uplink, and such subframe includes j OFDMA symbols.
How to choose the appropriate opportunity to transmit the MIMO midamble and transmit which format of the MIMO midamble will affect channel measurement effect, for this, there is no effective implementation method at present.